Thetis, one of the Nereids, was brought up by Hera. Both Zeus and Poseidon fall in love with her, but an oracle prophesied that the son born to Thetis would be more powerful than her father. Thus the gods hurried to marry her off to a mortal. She was married to Peleus, king of Phthia, and gave birth to Achilles. She left Peleus, but never lost interest in her son, whom she helped and gave advice all his short life.
See: Jean-Auguste-Dominique Ingres. Jupiter and Thetis.